In recent years, various types of sensors have been used in all fields. For example, hand movement correction apparatuses used in a digital still camera, digital video camera or the like, or lens position detection apparatuses used for zooming or automatic focusing may need a sensor having a function of performing position detection instantaneously with high precision. At the same time, with recent increasing demands for miniaturization of the entire apparatus miniaturization of the sensor may be required in itself. Further, sensors having such characteristics as extension of life and being hard to be affected by dust, oil (grease) and the like may be required.
In order to satisfy the above requirements, a position detection method using a magnetic sensor as the sensor is a well known technique.
For example, as the magnetic sensor, a method described in Patent Document 1 and the like mat be changed or revised. More specifically, as shown in FIG. 3 of Patent Document 1, the method discloses a technique that a moving part includes a magnet and the movement of the moving part is detected using a plurality of magnetic sensors.
The present inventors have hitherto discloses a position detection apparatus described in Patent Document 2 and so on. Presently, this position detection mechanism is widely used as a key part of a vibration compensation apparatus of a digital still camera.
There will now be described the principle and configuration of performing position detection using several magnetic sensors.
FIG. 13 shows a position detection method using Hall sensors 11 and 12 as a magnetic sensor.
In FIG. 13, a permanent magnet 23 is arranged opposite to the two Hall sensors 11 and 12 that are arranged with a predetermined distance. Respective Hall output voltages of the two Hall sensors 11 and 12 are varied according to a variation in magnetic flux density due to movement in a lateral direction (arrow direction). A differential value between Hall output voltages is processed by a differential signal processing circuit to detect a position of the permanent magnet 23. In the position detection, the movement direction of the permanent magnet 23 is parallel to a line along the two Hall sensors 11 and 12.
Typically, in order to reduce a burden of calibration, the size of the permanent magnet 23, the distance between the Hall sensors 11 and 12, and the distance between the Hall sensors 11 and 12 and the permanent magnet 23 are designed so that the differential value between the Hall output voltages is varied linearly contrast to the movement distance of the permanent magnet 23 in a lateral direction.
The configuration shows a satisfactory characteristic when the relative movement distance of the magnet and Hall sensors is several mm or less. Thus, the configuration is used as a key part of a vibration compensation apparatus of a single-lens reflex digital camera. However, when the movement distance is larger than several mm, there is a problem that whole mechanism becomes larger. Thus, practical use of the configuration cannot be reached.
Further, when position detection is performed in a wide temperature range with high precision, the position detection may be performed such that variation of a characteristic due to variations in ambient temperature of the Hall sensor and magnet is suppressed by using an output signal processing method described in Patent Document 6.
In a method of position detection with a narrow range, one-axis direction position detection may be performed using a magnet and a single Hall sensor arranged as shown in FIG. 6 of Patent Document 5, so as to reduce the number of components.
Also, in a method of position detection requiring high precision with a narrow range, position detection may be performed using specially-arranged two magnets as described in Patent Document 4.
In a method of position detection requiring high precision with a wide range, position detection may be performed using a special magnet as shown in Patent Document 3 such that linearity of the difference between Hall output voltages of the two Hall sensors contrast to the lateral movement distance of permanent magnet is improved.
Meanwhile, when position detection is performed with a wide range of approximately 10 mm that is required by the lens position detection apparatus used for zooming or auto focusing in a digital still camera or digital video camera, a method using an encoder is generally known. However, when an encoder is used, there is a problem that a complicated processing circuit including a counter for processing a signal outputted from the sensor. Further, when there occurs loss of synchronism between the movement device and encoder, a desired characteristic cannot be achieved, and thus the method is not suitable for high-speed movement objects.
As a method that is used for position detection with a wide range of approximately 10 mm and that does not include an encoder, there may be used a magnetic resistance element as shown in Patent Documents 7 and 8. This method is a well known technique that a rectangular shaped magnet (or a magnetic body) is inclined to a movement direction and a magnetic resistance element is arranged in a direction orthogonal to the movement direction. Thus, lateral movement of the moving body can be detected according to a variation of a longitudinal magnetic field.
[Patent Document 1] Japanese Patent Laid-Open No. 2002-287891
[Patent Document 2] WO 02/086694
[Patent Document 3] Japanese Patent Laid-Open No. 2005-284169
[Patent Document 4] Japanese Patent Laid-Open No. 2004-245765
[Patent Document 5] Japanese Patent Laid-Open No. 2002-229090
[Patent Document 6] Japanese Patent Laid-Open No. 2004-348173
[Patent Document 7] Japanese Patent Laid-Open No. 59-159578
[Patent Document 8] Japanese Patent Laid-Open No. 6-229708